1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device and, more specifically, to a manufacturing method of a semiconductor device that is suitable for miniaturization of a semiconductor device having a capacitor.
2. Description of the Background Art
FIG. 7 is a flowchart showing a former manufacturing method of a semiconductor device having a capacitor. In this former manufacturing method, first, a capacitor bottom electrode film is formed on a silicon wafer (step 10). Specifically, polysilicon containing phosphorus as an impurity is deposited on the silicon wafer by CVD.
Then, a bottom electrode of a capacitor is formed by properly patterning the bottom electrode film by photolithography and dry etching (step 12).
Then, a nitride film as an insulating film of the capacitor is formed on the bottom electrode (step 14). Specifically, the nitride film is deposited on the bottom electrode by CVD by using dichlorosilane (SiH.sub.2 Cl.sub.2) and ammonia (NH.sub.3) as materials.
FIG. 8 shows a series of processes that are executed in the insulating film (nitride film) deposition step. As shown in FIG. 8, in this step, evacuation of a reaction furnace, increasing of silicon wafer temperature, formation of a nitride film by CVD, and a purge are performed consecutively. In the former manufacturing method, the evacuation, the temperature increasing, and the purge are performed in a nitrogen atmosphere.
Upon completion of the insulating film formation, wet oxidation is performed on the surface of the insulating film (step 16). This step is intended to repair defects that are included in the nitride film (insulating film) to thereby improve the electrical characteristics of the capacitor and increase its reliability. In the former manufacturing method, the wet oxidation is performed by heating the silicon wafer at 800.degree. C.-900.degree. C. in water vapor that is obtained by mixing hydrogen and oxygen.
To activate the impurity that is contained in the bottom electrode, it is necessary to subject the silicon wafer to a heat treatment. In the former manufacturing method, the impurity in the bottom electrode can be activated by heat that is applied to the silicon wafer during the above wet oxidation.
After completion of the wet oxidation of the insulating film, a top electrode film is formed on the insulating film (step 18). In the former manufacturing method, the top electrode film is formed by depositing polysilicon that contains phosphorus at a concentration of about 5.times.10.sup.20 atoms/cm.sup.3.
The thus-formed top electrode film is then patterned properly by photolithography and dry etching into a top electrode of the capacitor (step 20).
Then, to sufficiently activate the impurities contained in the top and bottom electrodes, a heat treatment is performed on the silicon wafer at 800.degree. C.-900.degree. C. for about 30 minutes (step 22).
However, in semiconductor devices, there may occur a case that capacitors are manufactured after forming transistors on a silicon wafer. In such a situation, there may occur an event that when the above-described wet oxidation (step 16) and heat treatment (step 22) are performed in manufacturing capacitors, heat that is applied to transistors and their vicinities causes diffusion of impurities that are implanted in various parts of the transistors. In particular, if the size of the transistors is enough small, i.e., if the semiconductor device is sufficiently miniaturized, the diffusion may disable normal operation of the transistors.
In such semiconductor devices as a memory equipped with a logic circuit, one method of increasing the operation speed is to form a metal wiring (word lines and bit lines) under capacitors. In this case, if the temperature of the silicon wafer exceeds the heat resistant temperature of the metal wiring in manufacturing the capacitors, defects may occur in the metal wiring to render the semiconductor device inoperative.
For the above reasons, to miniaturize a semiconductor device or increase its operation speed, it is desirable that heat treatments in a capacitor manufacturing process be performed at as low a temperature as possible. In this respect, former manufacturing methods of a semiconductor device still have room for improvement.